The goal of this proposal research is to provide support and continued mentorship to facilitate the applicant's development into an independent scientific investigator in interstitial lung disease and lung immunology. This will be accomplished through a curriculum designed to obtain a solid basic science background involving hands on laboratory experience, regular didactic teaching, frequent presentations, and close mentoring by successful physician-scientists. The proposal will allow at least 75% of protected research time for the applicant. Using the research proposal as a platform, the applicant will gain expertise in number of fundamental scientific techniques including: the analysis of murine fibrotic lung disease, the generation of cell specific knockout mice and the assessment of macrophage and fibroblast function. This effort will involve a dynamic research group which functions in an overal university environment fostering cutting edge research. Research Project: Fibrotic lung diseases are a significant cause of morbidity and mortality for which effective therapies are lacking. The mechanisms that regulate unremitting pulmonary fibrosis are incompletely understood. Our laboratory has recently described a model of severe and progressive fibrosis in response to non-infectious lung injury. CXCR3 is the receptor for the IFNg-inducible chemokines CXCL9 (Mig), CXCL10 (IP-10) and CXCL11 (ITAC). These chemokines have been suggested to be important mediators of Th1 immunity. CXCR3 null mice develop severe and progressive fibrosis following treatment with intratracheal bleomycin relative to wild type control mice. Microarray analysis has identified a preponderance of genes associated with Th2 immunity expressed in the absence of CXCR3. In addition, we identified a number of genes that have been associated with the alternatively activated macrophage phenotype. These include Mannose Receptor, YM1 and Scavenger Receptor. The most prominent of the genes associated with an alternatively activated macrophage phenotype was a 36-fold induction in arginase-1. While alternatively activated macrophages have been implicated in mediating immunologically mediated tissue fibrosis, their roles in non-immune regulated processes are less clear. Arginase-1 is produced both by alternatively activated macrophages and fibroblasts in response to non-infectious lung injury. It has the potential to directly mediate fibrogenesis. Arginase-1 is responsible for the conversion of L-arginine to proline and polyamines. Polyamines are involved in cell proliferation while proline is a direct precursor of collagen. The role of arginase-1 expression by macrophages and fibroblasts in progressive fibrosis has not been explored. Based on our preliminary data, we hypothesize that arginase-1 expression in macrophages and fibroblasts is critical to the development of fibrosis after non-infectious fibrotic lung injury. We will test thi hypothesis in the following specific aims: AIM 1: Define the specific macrophage phenotypes recruited to the lung in CXCR3 null mice after non-infectious lung injury using a novel flow cytometric approach that distinguishes recruited and resident populations. AIM2: Determine the effects of targeted deletion of arginase-1 in macrophages and fibroblasts after non-infectious injury using a floxed arg-1 allele crossed with either a cre-recombinase strain that targets macrophages or fibroblasts. Collectively, this approach will allow us to dissect the role of arginase-1 production by macrophages and fibroblasts in the pathobiology of progressive pulmonary fibrosis.